1. Field of the Invention
The present invention relates to image processing apparatuses for prepress printing, such as RIP systems which create dot data representing images to be printed. More specifically, the present invention relates to assigning a multi-screening operation when creating the dot data.
2. Description of Background Art
In prepress printing systems a computer called the front-end is used in prepress processes to produce, edit, and layout the text, logos, images, pictures, illustrations, and other data parts composing the printed product, and thus output the edited layout data which is a set of data described in a page description language (hereinafter called “page description data”). Next, the edited layout data or the page description data undergoes a RIP process provided by a RIP system which is an image processing apparatus for prepress printing. In the RIP process, the page description data undergoes a rasterizing process (a RIP process in a narrow sense), and is converted to multi-valued bitmap data. Then the multi-valued bitmap data undergoes a halftone (screening) process, to be converted to dot data. In other words, an image represented by continuous gradation data is now represented by dot data. The screening process is specified by screen ruling or the number of screen mesh, dot shape and screen angle. In other words, the screen ruling, the dot shape and the screen angle determines a dot pattern in the prepared dot data. The dot data is then sent to an output device such as a plate recorder or digital printer, where the image represented by the dot data is recorded on a printing plate, paper or the like.
In such a prepress printing system as described above, when creating dot data through a screening process, there is a case in which a selected image(s) or object area(s) of the printed matter represented by the page description data must be screened by using a special dot pattern (screen ruling, dot shape and screen angle) which is different from a normal dot pattern to be assigned through a normal setting operation of the RIP system. Such a screening operation is called “multi-screening.”
When creating dot data in the RIP system through a multi-screening operation, settings for the multi-screening operation require special information that relates a usable dot pattern to an output device which can make output by using this specific dot pattern. Conventionally, this information essential to the multi-screening operation (hereinafter called “multi-screening information”) is not viewable unless a set of operations specific to the RIP system is performed. Furthermore, the multi-screening information is described in an uncommon format, stored within the RIP system, and is lacking in portability. As a result, any addition or other forms of revision made to the multi-screening information in the RIP system creates difficulties in maintaining information link between the input data creation process side working on the creation of edited layout data and the output operation process side working on the creation of dot data.
For this limitation in the conventional systems, instructions for multi-screening operations cannot be given directly from the input data creation process side. Instead, in order to do so, it is necessary to make an operation request or create links of instructions from the input data creation process side to the output operation process side. Such a task of linking instructions and making requests increases not only the amount of work in the process but also chances of mistakes.